In a working machine, such as earth moving machinery, the internal combustion engine (ICE) supplies power for propelling the working machine in the forward and reverse directions. The ICE also supplies power for the actuation of all of the installed machine implements. A transmission is coupled to the engine and transmits power from the engine to the drive train to propel the working machine in the desired direction and speed.
The working machine operates at relatively low speeds and in cyclical work routines, thus there is a need to control speed precisely at low speeds and to adjust it infinitely throughout the full working range.
It is desirable to utilize a continuously variable transmission (CVT) and manage the transmission ratio to thereby save engine power for the actuation of the implements and also to provide a continuously variable power flow through the transmission to improve machine productivity.
Furthermore, CVTs provide stepless shifting in working machine operation, allowing the engine to operate at an optimal speed range. This results in lower fuel consumption or lower emissions than the fuel consumption or emissions of a conventional transmission. However, typical CVTs suffer from lower efficiency or lower torque handling capabilities than conventions transmissions.
It would therefore be advantageous to combine the variability of the CVT with the efficiency of a mechanical transmission, to provide potential benefits for off road vehicles specifically. These so-called power split drives are known, but the technology is still in development.
In a power shift drive, a planetary gear set (PGS) is combined with a mechanical stepped path resulting in the coupling of a continuous variable speed control with a simultaneous high efficiency level from the mechanical gears. Unfortunately, known power shift drives capable of meeting speed and torque requirements suffer from high complexity and cost.
The present invention is directed to overcoming one or more of the problems as set forth above.